Method for eliminating the need to zero and calibrate a power meter before use

ABSTRACT

An improved power sensor having an input connector connected to an input port having a center pin and a ground side; an amplifier; first and second detectors; and a thermal stabilization system, including a thermal mass disposed between the ground side of the input connection and the detectors, a ground plane for holding the temperature of thermally sensitive components constant to within 2 degrees C., and a thermal impedance disposed between the center pin of the input port, preferably including a splitter and at least one DC capacitor, and a temperature sensor disposed on the ground plane.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a divisional patent application which claimsthe benefit of U.S. Utility patent application Ser. No. 11/869,594 filedOct. 9, 2007 (Oct. 9, 2007,) which application claims the benefit ofU.S. Provisional Patent Application Ser. No. 60/828,587 filed Oct. 6,2006 (Oct. 6, 2006.)

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

THE NAMES OR PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT Disc

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to power meters, and morespecifically to means to ensure power meter accuracy, and still moreparticularly to a method and apparatus that eliminates the need tocalibrate or zero a power meter.

2. Discussion of Related Art Including Information Disclosed Under 37CFR §§1.97, 1.98

For over 50 years all RF and microwave power meters have provided ameans to zero and calibrate the meter before use. For bench use, theneed to zero and calibrate is a source of inconvenience and irritation.It can also be a source of error. This requirement to zero and calibratea power sensor becomes more problematic in large systems. In rackedsystems the need to zero and calibrate contributes uncertainty, addshardware and engineering, and increases software complexity and cost.

The use model typical for power meters and sensors is: (1) remove thepower sensor from all RF and microwave power sources; (2) zero themeter; (3) if required, connect the power sensor to a calibrated source;(4) if required, calibrate the power sensor; and (5) remove the powersensor from the calibrator. After taking these measures, the power meteris purportedly ready for use, and it is connected to a measurement port.

Some newer sensors introduced internal switches allowing an internal (tothe sensor) load and reference to be switched in or out for purposes ofzeroing and calibration. And while this approach mitigates some problemsit causes others. The problems mitigated are the need for the user tomake/break electrical connections during calibration and zeroing.However, it very nature introduces additional expense. These switchesintroduce additional uncertainty. In addition, the process of switchinginduces discontinuities in the signal paths. These discontinuities canbe the source of unwanted reflections especially in systems withsensitive receivers.

Calibration before use should not be confused with annual calibration.Calibration before use (if required) is accomplished by connecting thepower sensor to a calibrated reference after it has been zeroed. Thissource is a part of the power meter. It is most commonly a 1 mW, 50 MHzsource. Zeroing or calibration before use is typically recommended whenambient temperature changes by about 5° C.

To understand how zeroing and calibration affects system hardware andsoftware design, it is useful to consider a simple example. Assume amodest automated system with a number of paths, such as the system 100one shown in FIG. 1, which includes an input (start) path 110, a numberof circuit elements and devices 120, and an output (end) path 130. Allmeasurements using these paths must be path loss compensated. Designersof automated systems want to minimize user interaction and testexecution time.

In practical systems, path loss requires periodic measurement. Path lossis generally determined by taking the difference between twomeasurements. This implies that one measurement must be taken at pointsproximate each end of the path, and these points must be accessible tothe measurement device. The low cost and relative accuracy of powermeters make them a good choice for path loss measurements.

However, entirely automated path loss measurement presentscomplications, many of which are related to the need to zero andcalibrate the power meter/sensor.

The following sets out a path loss calibration algorithm which requiressome user interventions and is not concerned with minimizing userinteraction or speeding up overall measurements:

User removes sensor from all system connections

-   -   User zeros the sensor    -   If calibration is required        -   User connects sensor to reference        -   Calibrates the sensor    -   End if    -   User connects sensor to input measurement point    -   For each frequency        -   Make measurement    -   Next Frequency    -   User connects sensor to the output measurement point    -   For each frequency        -   Make measurement    -   Next Frequency    -   For each frequency        -   Apply difference between input and output to path correction        -   Apply systematic or known offsets to path correction    -   Next Frequency

In newer sensors with internal switches, the points requiring the userto remove and/or connect the sensor in the process outlined above wouldbe replaced with commanding the sensor to switch in the load orreference as needed. Clearly this is an advantage in terms of speed andallows the system to be more automated. However, there is a clear tradeoff in terms of additional expense and the discontinuity issues andchanges in system match are still present.

This is a simplified path calibration process showing all userinterventions in bold typeface. What is not noted is the need for theuser to pay close attention to the proximity and routing of signals andthe placement of the power meter and sensor in the system. This will bedealt with later in this disclosure.

A completely automated process is far more desirable. However, becausepower meters require zeroing and/or calibration, complete automation ismore expensive and more difficult to achieve. The inventive automatedmethod and apparatus does not depart substantially from theuser-mediated process outlined above. However, the design of theinventive system is modified such that the system breaks the sensorconnection to the system and then makes the connections to the sensorreference, and input and output measurement points. These connectionsare managed through switches.

Consider the first user interaction from the sequence outlined above:User removes sensor from all system connections: For presently availablesensitive sensors (sensitivities below −65 dBm) the sensor is oftenconnected to a port that guarantees signal levels lower that −80 dBm.This can be done by connecting the power sensor to a port terminatedinto a 50Ω load. This sometimes requires the addition of a microwaveswitch. This switch must be managed by software and the additionaluncertainty and correction must be accounted for in the measurement.

What is generally not recognized is the need to keep track of the lastzero and calibration in the system software. On complex systems thismust be done across many tests and measurements. The alternative todoing this is to zero and calibrate before each major test. This causesextra wear on switches and can be significant in some case and costsextra measurement time since zeroing and calibration (in relative terms)a time-consuming measurement.

The next user interaction is even more problematic: User connects sensorto reference. The power meter sensor is specified based on theassumption that during calibration the sensor is connected directly tothe calibration source. Some manufacturers recognize the significance ofthis problem and have included references internal to the sensors. Itshould be clear that the calibration reference must be routed to everysensor or every measurement point must be routed to a single sensor. Asa result there will be more switches, greater uncertainty and greatercost.

There is one other, perhaps more subtle, problem associated withcalibration: The existence of the calibrator and the need to make itextremely accurate forces the manufacturer of the power meter to fix theconnector type and sex. This decision is not without negative impact onthe system.

By fixing the type and sex of the connector of the calibrator, themanufacturer also fixes the type and sex of the power sensor. Thisalmost always forces the system designer to employ adapters between thesystem and the power meter. Every adaptor adds further uncertainty tothe measurements of the system. This small initial uncertainty may havean unexpectedly larger impact because it is seen in subsequentuncertainty calculations.

The next user interaction is: User connects sensor to input measurementpoint. Again, this intervention poses additional problems. In most RFand microwave systems the measurement should be as close as possible tothe components being measured. In this case the paths are likely buriedinside a complex system (path routing accomplished with a switchmatrix). The paths within the system are generally not accessible. Theonly alternative in most systems is to bring the measurement port out tothe power sensor.

This can add significant path length to signals that may not be able totolerate the associated loss or mismatch. This poses serious problemsfor system developers. The result is often serious compromises inaccuracy test time and it adds complexity and hardware costs.

As a practical matter the relationship of zeroing and calibration totemperature can be shown to be almost exclusively associated with thesensor (or detector) itself. In other words, the meters havetraditionally had little impact on zero and calibration drift issues.This can be demonstrated using the venerable Agilent Technologies, IncHP432A and HP478A in their normal configurations. Experiments show thatan HP478A (connected to an HP432A) in a normal environment will requirecoarse and fine zeroing after being turned on.

During roughly the first half hour after it has been turned on, theHP478A will need to have this process repeated about every 4-5 minutes.It may require zeroing more often if the most sensitive ranges are used.As the device stabilizes it still requires a zeroing and calibrationevery half hour, and more often if the environment is less wellcontrolled.

In addition, zero and calibration will be required more frequently ifthe device is handled. Simply picking up a newly zeroed device willcause significant drift of the zero on the lower ranges. This sameroutine can be repeated with other sensors and RF detectors.

On the other hand, if the HP478A power sensor is placed in a temperaturecontrolled environment, it can remain zeroed indefinitely. Experimentsshow that an HP478A that is heater stabilized temperature to within+/−½° C. will remain zeroed indefinitely. In experiments conducted bythe present inventors, however, only the HP478A was temperaturestabilized; the HP432A power meter was not temperature stabilized.During this time ambient temperature ranged from about 50 F to more than80 F.

Accordingly, despite the fact that awareness of the problem and itssource has existed for more than fifty years, power meters have remainfundamentally unchanged.

The foregoing systems reflect the current state of the art of which thepresent inventors are aware. Reference to, and discussion of, thesesystems is intended to aid in discharging Applicants' acknowledgedduties of candor in disclosing information that may be relevant to theexamination of claims to the present invention. However, it isrespectfully submitted that none of the prior art methods or devicesdisclose, teach, suggest, show, or otherwise render obvious, eithersingly or when considered in combination, the invention described andclaimed herein.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a method and apparatus that eliminatesthe need to calibrate or zero a power meter. Because variation inphysical properties is great, it is difficult to apply a quantitativeapproach to this solution. Fortunately, experience indicates thatminimal experimentation results in excellent results in short order.

The present invention combines techniques that were present on the firstpower meters (in the 1950s) but adds novel elements and method steps.The inventive elements include: (1) adding thermal isolation between thedetector at the measurement port; (2) measuring detector temperaturedirectly or as directly as possible (some designs measure thetemperature of the “sensor”); (3) adding gain in low signal level paths,using (a) linear amplifier, and (b) a log detector.

In this context log detector generally comprises a detector followed bya logging amplifier. In general gain may be present before the detectoras part of the detector or between the detector and the loggingamplifier. The preferred embodiment used an integrated device employingthe progressive compression technique over a cascaded amplifier chain.However, any function may be used in place of the log detector(function) provided range compatibility, monotenicity and adequate powerresolution is achieved. When operated outside of its square law range,the Agilent E4412A Wide Dynamic Range CW Power Sensor is example of sucha function; however, it can only measure CW (discussed below) and doesnot address key aspects of this invention. The preferred embodiment usesthe AD8318 manufactured by Analog Devices Inc.

Historically, log detectors have not been used in RF and microwave powermeasurement instrumentation for purposes of measuring accurate power.The primary reason for this has to do with the fact that, up untilrecently, RF power has been made with detectors providing a voltageproportional to power. The primary reason for this was the fact thatmeasurement integration, to support pulse and other non-CW (ContinuousWave signal operating at a fixed unmodulated frequency), had to be donein hardware. And correct integration requires each of the signalcomponents to be proportional to power.

Another import aspect to the log detector has to do with the managementof signal bandwidths; there are three places to set the bandwidth.Setting them correctly is imperative to measure power correctly.Bandwidth will be discussed later. At the outset, however, there isfirst a discussion on integration using the diode topology similar tothat employed in the Agilent E4412A.

Power measurements have been made using detector diodes operating intheir square law region, or that region of the detection curve wheredetected voltage is proportional to RF input power. As power isincreased the detected output of the diode begins to compress and outputaccuracy suffers considerably. In recent years, the application ofcomputing power allows a technique often referred to as compressioncorrection. Compression correction works well provided the sensor ismeasuring CW power (power concentrated at a Continuous Wave signaloperating at a fixed unmodulated frequency). This technique has beenemployed in commercial power sensors like the Agilent E4412A WideDynamic Range Power CW Power sensor. The problem is the technique islimited to CW signals.

When measurement of complex signals, such as pulsed RF found radar ormany of the CDMA, W-CDMA, WiMAX, AM, FM, etc. signals found in wirelessand hard-line communications today, signals cannot be measured correctlywhen applying compression correction. This is because in order tocorrectly measure the RF power the total of all power components withinthe signal bandwidth must be integrated or added together. A diodedetector operating in square law does the integration in hardware usingthe integrating capacitor following the detector. The integrationcapacitor sets the video bandwidth of the detector and all frequencycomponents outside the video bandwidth are integrated by the integratingcapacitor. Off course all signals inside the video bandwidth passthrough.

When the detector is in square law, the components are proportional topower and the integrated components are proportional to power. Thus bothCW and complex signals maintain the same relationship between measuredand actual power.

When the detector is outside of square law, the components are no longerproportional to power and thus when integrated the result is notpropositional to power. In fact each complex signal format generallyresults in a different integrated value for a given power level. Thusboth CW and complex signals do not maintain the same relationshipbetween measured and actual power outside of square law.

A log detector suffers from the same integration relationship problem aswith the diode detector operating in compression just described.However, by applying filters at the correct points in the measurementchain and making sure correct power integration occurs, a log detector(and diodes in compression, etc) can be used and CW as well as thevarious complex signal formats may be correctly measured using the samelinear integration relationship.

The invention has three filters. (1) A detector filter, the filterassociated with the detector. Usually set by the integrating capacitorfollowing the detector. This capacitor integrates linear power measuredat the detector when the detector is operating in its square law region.(2) The bandwidth of the logging amplifier (or other non-linearmonotonic stage or component). The capacitance (or equivalentcapacitance) determines the bandwidth of this stage. This capacitor willlinearly integrate whatever signal appears outside its bandwidth. Andlike the diode operating in compression, correct power integration forsignals outside the logging amplifier's bandwidth cannot occur in thisfilter. (3) The bandwidth of the ADC (analog-to-digital converter). Thecapacitance (or equivalent capacitance) of the ADC sets the acquisitionbandwidth. Because the ADC is receiving the logging amplifier signal,which cannot be integrated correctly, digitized signals are inherentlynonlinear. Thus correct power integration cannot occur for signalsfalling outside the ADC's filter bandwidth.

With this in mind, for a practical implementation designed to measurepower for both CW and complex signals, there are two ways to properlymanage the filters (1) Unlimited video bandwidth approach practicalvideo bandwidth limit for measuring microwave power is on the order ofhundreds of MHz; as frequency increases so will the bandwidth). (2)Limited video bandwidth approach, such as implemented in the preferredembodiment.

In the unlimited video bandwidth approach, bandwidth is set by thedetector bandwidth, which correctly integrates power at the point ofdetection. The detector must provide a signal proportional to power.Power cannot be integrated by the logging amplifier and therefore thelogging amplifier's bandwidth must be greater than the detectorbandwidth. In this case CW and complex average power measurements forvery wideband signals can be made. For signals falling inside thedetector bandwidth, appropriate data acquisition techniques and DSPtechniques must be applied. The DSP is similar to the DSP used for thelimited video bandwidth case to be described below. The detectorbandwidth also sets the video bandwidth for time domain or pulseprofiling as well as the bandwidth whereby a variety of DSP functions(histograms, etc.) can be employed.

In the limited bandwidth case, bandwidth is made as wide as possible andis therefore typically set by the logging amplifier bandwidth or the ADCbandwidth. In either case power integration can occur on a logged signal(either the logging amplifier or the ADC). Thus, only accurate powermeasurements can be made for signals falling within the smaller of thelogging amplifier or ADC bandwidth. In the preferred embodiment, thelogging amplifier bandwidth is set to approximately 20 MHz and the ADCbandwidth is set to 10 MHz. Thus the preferred embodiment is limited tocorrectly measuring signal in a 10 MHz bandwidth. The detector's largesignal bandwidth exceeds 50 MHz and its small signal bandwidth exceeds500 MHz. In this case signals falling within the 10 MHz pass through thevideo bandwidth of the system and are digitized and of course thesedigitized samples are correctly measured. To get an accuraterepresentation, as with any DSP acquisition system, many samples must bemade.

The result is a series of samples varying with time and as a function ofthe signal being measured. To determine the correct measured power thekey is to correctly convert the series of samples into a correct powermeasurement. Because the samples pass through the non-linear loggingamplifier simple integration cannot produce the correct powermeasurement. Integration can only be correctly applied to the correctedlinear power samples. Thus appropriate DSP consists of applying powercorrection to the samples and then integrate. Of course integration isdone on samples converted to their linear in watts (or milliwatts, etc.)form.

If a time domain or pulse profile plot or other signal processing isdesired, the samples can be used after correction is applied.

The present invention also employs design elements and techniquespresent in older designs. The primary element used in almost all pastdesigns includes use of relatively large thermal mass. Other techniqueshave been used in other sensors to mitigate the impact of thermalchanges on measurements. This includes the characterization, measurementand compensation of ambient temperature or other the overall temperatureof the sensor.

It is important to note that measuring ambient temperature or sensortemperature may help mitigate the issue of zero drift. It isinsufficient by itself. This is largely due to uncontrolled thermalgradients that are allowed to exist between the point of temperaturemeasurement and the detector. This means that at low levels the detectedpower will follow local temperature changes more closely than changes inpower level.

This fact is evident from experiments using the HP432A and HP478A. Addto these facts that even when the HP478A is used in carefully controlledambient environments (free air but well controlled) the HP478A still hassignificant short term and sometime long term zero drift problems.

The experiments also show that when the entire HP478A is entirelyenclosed in a highly controlled environment both short term and longterm zero drift was eliminated. This same sort of drift is present indetectors.

Management, measurement (and compensation), and mitigation of theeffects of temperature is key. All this is consistent with generalmetrology knowledge. It is also important to recognize the primary typesof temperature instability that force zeroing include: (1) short terminstabilities (a second or less to several seconds); and (2) longer terminstabilities (more than several seconds).

Short term instabilities are caused by a number of factors. Handling,changes in the temperature of connections, rapid changes in ambienttemperature, the movement of exhaust air from other equipment over thesensor body and so on. These short term changes tend to affect the mostsensitive power measurements or ranges.

Long term stabilities tend be associated with the warm-up (powerdissipation of the unit itself), ambient temperature changes, andconnection to very cold or very warm connector. These changes tend toaffect all ranges and power levels.

The foregoing summary broadly sets out the more important features ofthe present invention so that the detailed description that follows maybe better understood, and so that the present contributions to the artmay be better appreciated. There are additional features of theinvention that will be described in the detailed description of thepreferred embodiments of the invention which will form the subjectmatter of the claims appended hereto.

Accordingly, before explaining the preferred embodiment of thedisclosure in detail, it is to be understood that the disclosure is notlimited in its application to the details of the construction and thearrangements set forth in the following description or illustrated inthe drawings. The inventive apparatus described herein is capable ofother embodiments and of being practiced and carried out in variousways.

Also, it is to be understood that the terminology and phraseologyemployed herein are for descriptive purposes only, and not limitation.Where specific dimensional and material specifications have beenincluded or omitted from the specification or the claims, or both, it isto be understood that the same are not to be incorporated into theappended claims.

As such, those skilled in the art will appreciate that the conception,upon which this disclosure is based may readily be used as a basis fordesigning other structures, methods, and systems for carrying out theseveral purposes of the present invention. It is important, therefore,that the claims are regarded as including such equivalent constructionsas far as they do not depart from the spirit and scope of the presentinvention. Rather, the fundamental aspects of the invention, along withthe various features and structures that characterize the invention, arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the presentinvention, its advantages and the specific objects attained by its uses,reference should be made to the accompanying drawings and descriptivematter in which there are illustrated the preferred embodiment.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be better understood and objects other than those setforth above will become apparent when consideration is given to thefollowing detailed description thereof. Such description makes referenceto the annexed drawings wherein:

FIG. 1 is a schematic showing a typical system 100 in which path losswould be expected;

FIG. 2 is a table 200 comparing voltage changes within a −20 dBm to −70dBm range as detected by a linear detector versus a log detector; and

FIG. 3 is a schematic view showing the principal elements comprising thepower sensor of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 3, the first step in providing the improved powermeter of the present invention is to isolate the incoming signaldetector from the measurement port. Specifically, there is a need toensure that any thermal transient that appears on the center conductorof the input port is not allowed to propagate to the detector. Capableengineers frequently design sensors for maximum sensitivity. Doing thisrequires the sensor be connected to the incoming signal with as littleloss as possible. This also means the detectors are directly accessibleto those same temperature changes.

The inventive design preferably includes at least one low lossattenuator or power splitter disposed between the incoming signal andthe detector. As the number of thermal impediments between the incomingsignal and the detector are increased, short term sensitivity isimproved.

The next step is to add temperature monitoring to the detectors or tocompletely stabilize the detector temperature, preferably the former.There are three basic ways to do measure temperature of the detector:(1) by using an RF detector with temperature monitoring (such as an theAD8318 by Analog Devices used in the preferred embodiment); or (2) byusing a detector die with a pair of detectors, wherein one detector isused for temperature measurement; or (3) by using a detector in closeproximity and low thermal impedance to a temperature measuring device.

Accurate temperature readings are not critical, but repeatability andsensitivity are. One must be able to detect changes as small as 0.5° C.Circuit designs meeting these criteria are numerous.

The second step is to minimize the rate of change of thermal effects.This serves to reduce the rate of change of the thermal gradientsbetween temperature sensitive elements critical to measurement. It isimportant the thermal gradient be stable enough to hold the temperatureof detectors, amplifiers, and other devices constant; specifically tohold their temperature to within a constant 1-2 degrees with respect toa thermally stabilizing mass.

For example, if the temperature sensitive elements in the sensor are anamplifier and a detector, the temperature gradient between theseelements and some ambient temperature should be measured. In otherwords, the largest temperature difference should be found. Then ambienttemperature should be changed and the temperature gradient re-measured.The length of time it takes to stabilize should be noted, and it will beclear that the new gradient is about the same as the old gradient andthe temperature of the devices is constant with respect to each otherand a thermally stabilizing mass.

Having done this, the performance of all the thermally sensitiveelements are coordinated and compensated. Experiments show that if thisis done properly, if one point on this thermal plain can be compensated,then all points can be compensated.

Finally, a method is employed to test the repeatability of the sensorfor given temperatures. This is commonly done in the industry. It ismost easily done by placing the sensor in a temperature controlledenvironment and measuring the indicated power relative to temperatureover the temperature range and power range of interest. If this resultsin repeatable measurements, then the long term temperature changes arenow manageable.

In most instances it is insufficient to measure temperature only.Cross-referencing temperature and power may be necessary.

Next, a correction table is developed and employed to cross referencethe correction of power readings for a range of temperature. Thesetables, like many temperature correction tables can be stored in ROMwith the sensor. This mitigates the long term temperature issues andmany of the short term changes. The effects of temperature on the lowestlevel signals may still be evident.

The last step deals with very small, fast changes in temperature. Thosewith skill in the art understand that this area concerns the last 10-15dB of sensitivity. The problem is easily understood when one considersthat short term variation in the diode junction voltage is nearly thesame as the changes in detected voltage. Two options are possible: (1)control the variation (e.g. by using an oven sufficiently large mass,with a low thermal impedance to the detector); (2) avoid using thisportion of the diode range.

Either approach may be used, but it is preferable to avoid using thisportion of the dynamic range of the diode. This is most easilyaccomplished by amplifying the signal prior to detection. The preferredembodiment uses the AD8318, which is a log detector employing theprogressive compression technique over a cascaded amplifier chain. Thepreferred embodiment also contains a preamplifier at the RF input.

The value of the log detector over a linear detector is readily evident.The log detector supplies a voltage proportional to the log of power.Also, most log detectors also supply some gain. The linear detectorsupplies a signal that is proportional to the power. While this iswidely understood in the industry a brief demonstration is appropriate.

To demonstrate the advantage, assume a linear detector and log detectoroperate output the voltage range (say 0.0 volts to 1.0 volt) but theiroutputs are scaled according to their respective functions (linear andlog). Furthermore, assume both operate over −70 to −20 dBm. Ignoring thenon-linear nature of these diodes for simplicity: (1) for the lineardiode, a −70 dBm to −65 dBm change in power results in change in outputvoltage of about 0.3 μV; (2) for the log detector, a −70 dBm to −65 dBmchange in power results in change in output voltage of about 0.1V.

This difference represents a 4000:1 ratio at low levels. Clearly thereis a tradeoff to be made. Using a log detector in a power sensor hasbeen viewed as problematic. As discussed above the modulated videooutput of a log detector cannot be directly averaged (integrated) usingfilters. This is readily remedied by converting the digitized log outputfrom dBm to mW then averaging digitally as already described. This goesa long way in managing short term temperature changes.

The next step is to add an amplifier for low level measurements. Whilesome noise figure is sacrificed, additional immunity to thermal noisevariation is addressed. As an illustration, consider the table 200 shownin FIG. 2. In this table, the change in voltage (for the lineardetector) between −70 and −60 dBm is about 0.09 mV. The change involtage between −60 and −50 dBm for the same detector is about 0.9 mV.Assuming that PN junction voltage changes of a few millivolts per degreeC., it is easy to see that this additional gain will provide someadditional immunity to short term, low level temperature variation.

Still referring to FIG. 3, according to the foregoing method steps,there is provided a novel power meter/temperature sensor of the presentinvention 300, which comprises a housing 310 having a connector for ananalog RF input signal 320, which is split by a splitter 330 into alower sense path 340 and a high sense path 350. The signal in the lowsense path is fed through a blocking capacitor 360 and then anattenuator 370 before being fed into a log detector 380 and temperaturesensor 390 having a thermal mass disposed on the ground plane 400. Thehigh sense path is likewise fed through a blocking capacitor 410 andthen an amplifier 420, such as an NBB-312, produced and sold by RF MicroDevices, Inc. of Greensboro, N.C., which is a cascadable broadbandgallium arsenide (GaAs) monolithic microwave integrated circuit (MMIC)amplifier. That signal then passes on to a log detector 430 andtemperature sensor 440 having a thermal mass 450 disposed on the groundplane.

The analog outputs 460, 470, 480, and 490 from the detectors and sensorsare fed into an analog to digital converter 500, such as an AD7655,produced and sold by Analog Devices of Norwood, Mass., which is a lowpower four-channel, 16-bit analog/digital converter with a 0-5V voltagerange for the analog input and uses a single 5V power supply. Thedigital output 510 is sent to a microcontroller 520, which in apreferred embodiment is a Cypress CY7C68013A, by Cypress SemiconductorCorporation of San Jose, Calif. The CY7C68013A is a low-power USB 2.0microcontroller that integrates a USB 2.0 transceiver, serial interfaceengine, enhanced 8051 microcontroller, and a programmable peripheralinterface in a single chip. The CPU is programmed to acquire thedigitized samples and transfer them to a computing platform, whichpreferably operates Windows XP, but which may utilize any of a number ofsuitable operating systems currently in use in the industry. A set ofsoftware programs residing on the computing platform perform theabove-described DSP computations—scaling, averaging (integration),compensating, temperature change detection and time determinations, andcorrection table cross referencing to correct power readings for a rangeof temperatures. (of course the DSP functions could in general reside ineither the Windows XP computing platform or equivalent or in an impededcontroller operating in the device.)

The above disclosure is sufficient to enable one of ordinary skill inthe art to practice the invention, and provides the best mode ofpracticing the invention presently contemplated by the inventor. Whilethere is provided herein a full and complete disclosure of the preferredembodiments of this invention, it is not desired to limit the inventionto the exact construction, dimensional relationships, and operationshown and described. Various modifications, alternative constructions,changes and equivalents will readily occur to those skilled in the artand may be employed, as suitable, without departing from the true spiritand scope of the invention. Such changes might involve alternativematerials, components, structural arrangements, sizes, shapes, forms,functions, operational features or the like.

Therefore, the above description and illustrations should not beconstrued as limiting the scope of the invention, which is defined bythe appended claims.

1. A power sensor having thermally sensitive components, comprising: aninput connector connected to an input port having a center pin; at leastone detector having a detector bandwidth for receiving an RF signal,each of said at least one detector producing a detected signal; at leastone temperature sensor for measuring the temperature of the thermallysensitive components and producing a temperature signal; ananalog-to-digital converter having a bandwidth, said analog-to-digitalconverter for receiving the detected signals and producing digitizeddata; thermal stabilization means for thermal stabilization of said atleast one detector; and at least one signal compression means disposedprior to said analog-digital-converter, said signal compression meansfor receiving the detected signals from said at least one detector andproducing a compressed signal having a signal compression bandwidth;wherein the power sensor is configured for limited bandwidth operationand said detector bandwidth is wider than said signal compressionbandwidth, and wherein the limited bandwidth is the resulting bandwidthwhen said signal compression bandwidth and said analog-to-digitalconverter bandwidth are combined.
 2. The power sensor of claim 1,further including a microprocessor having software including digitalsignal processing algorithms for applying temperature compensating powercorrection and digital integration to said digitized data and producingcorrected power measurements.
 3. The power sensor of claim 1, whereinsaid thermal stabilization means comprises: a large thermal massdisposed between a ground side of said input connector and saiddetectors; and a ground plane for the thermally sensitive components,said ground plane holding the thermal gradient constant to ensurethermal sensitive components are held to within 2 degrees C. withrespect to said thermal mass.
 4. The power sensor of claim 3, whereinsaid thermal mass is configured to attenuate or filter thermaltransients before they reach the thermally sensitive components in saidpower sensor.
 5. The power sensor of claim 4, wherein said thermal massis an aluminum disk.
 6. The power sensor of claim 5, wherein saidthermal stabilization means comprises at least one splitter and at leastone DC blocking capacitor.
 7. The power sensor of claim 1, including atleast two temperature sensors.
 8. The power sensor of claim 7, whereinsaid temperature sensors comprise: a temperature measuring deviceproducing a monotonic signal with respect to the temperature of saidthermal stabilization means; and conditioning circuitry producing saidtemperature signal.
 9. The power sensor of claim 8, wherein saidtemperature measuring device is selected from the group consisting of anintegrated circuit, a diode, a transistor, a thermister, a thermocouple,a temperature sensitive metal, and a metal film, or some combinationthereof.
 10. The power sensor of claim 7, wherein, said temperaturemeasuring device is integrated into said at least one detector.
 11. Thepower sensor of claim 1, further including at least one RF amplifierhaving gain.
 12. The power sensor of claim 1, including at least twodetectors.
 13. The power sensor of claim 1, wherein said signalcompression means produces a compressed signal detected by saidanalog-to-digital converter.
 14. The power sensor of claim 13, whereinsaid signal compression means comprises a non-linear component thatcompresses the detected signal and produces a compressed signalmonotonic with respect to the detected signal.
 15. The power sensor ofclaim 14, wherein said non-linear component comprises a device selectedfrom the group consisting of a logarithmic amplifier, alogarithmic-logarithmic amplifier, a peak detecting diode, a diodeoperating between peak and square law mode, a variable gain amplifierconfigured to provide said non-linear component operation, a peakdetecting transistor, and a transistor operating between peak and squarelaw mode.
 16. A power sensor having thermally sensitive components,comprising: an input connector connected to an input port having acenter pin; at least one detector having a detector bandwidth forreceiving an RF signal, each of said at least one detector producing adetected signal; at least one temperature sensor for measuring thetemperature of the thermally sensitive components and producing atemperature signal; an analog-to-digital converter having a bandwidth,said analog-to-digital converter for receiving the detected signals andproducing digitized data; thermal stabilization means for thermalstabilization of said at least one detector; and at least one signalcompression means disposed prior to said analog-digital-converter, saidsignal compression means for receiving the detected signals from said atleast one detector and producing a compressed signal having a signalcompression bandwidth; wherein the power sensor is configured forunlimited bandwidth operation and said detector bandwidth is narrowerthan said signal compression bandwidth, and said detector bandwidth isnarrower than said analog-to-digital converter.
 17. The power sensor ofclaim 16, further including a microprocessor having software includingdigital signal processing algorithms for applying temperaturecompensating power correction and digital integration to said digitizeddata and producing corrected power measurements.
 18. The power sensor ofclaim 16, wherein said thermal stabilization means comprises: a largethermal mass disposed between a ground side of said input connector andsaid detectors; and a ground plane for the thermally sensitivecomponents, said ground plane holding the thermal gradient constant toensure thermal sensitive components are held to within 2 degrees C. withrespect to said thermal mass.
 19. The power sensor of claim 18, whereinsaid thermal mass is configured to attenuate or filter thermaltransients before they reach the thermally sensitive components in saidpower sensor.
 20. The power sensor of claim 19, wherein said thermalmass is an aluminum disk.
 21. The power sensor of claim 19, wherein saidthermal stabilization means comprises at least one splitter and at leastone DC blocking capacitor.
 22. The power sensor of claim 16, includingat least two temperature sensors.
 23. The power sensor of claim 22,wherein said temperature sensors comprise: a temperature measuringdevice producing a monotonic signal with respect to the temperature ofsaid thermal stabilization means; and conditioning circuitry producingsaid temperature signal.
 24. The power sensor of claim 23, wherein saidtemperature measuring device is selected from the group consisting of anintegrated circuit, a diode, a transistor, a thermister, a thermocouple,a temperature sensitive metal, and a metal film, or some combinationthereof.
 25. The power sensor of claim 23, wherein, said temperaturesensor is an integrated part of said at least one detector.
 26. Thepower sensor of claim 16, further including at least one RF amplifierhaving gain.
 27. The power sensor of claim 16, including at least twodetectors.
 28. The power sensor of claim 16, wherein said signalcompression means produces a compressed signal detected by saidanalog-to-digital converter.
 29. The power sensor of claim 28, whereinsaid signal compression means comprises a non-linear component thatcompresses the detected signal and produces a compressed signalmonotonic with respect to the detected signal.
 30. The power sensor ofclaim 29, wherein said non-linear component comprises a device selectedfrom the group consisting of a logarithmic amplifier, alogarithmic-logarithmic amplifier, a peak detecting diode, a diodeoperating between peak and square law mode, a variable gain amplifierconfigured to provide said non-linear component operation, a peakdetecting transistor, and a transistor operating between peak and squarelaw mode.